As someone who was part of the rollout of HTTP2 for a $large_website, I can confirm that "this will harm mobile performance" was outright and flatly rejected. This included people who were our reps on the w3c. I just had to sit there and wait for the real world metrics to come in
"multiplexing will remove bottlenecks!"
"benchmarks prove that its faster!"
"you just don't understand how TCP works"
"the people at google are very smart, what do you know?"
"server push will reduce latency"
etc etc etc.
We even had the graphs of page size over time (going ever up) and average usable bandwidth (not keeping up, especially on mobile) None of that mattered until the rollout had a real world effect on our performance.